Retrogradation

Retrogradation is a general term used in various scientific fields to describe the reversal of a process or the return of a system toward a previously established state, often accompanied by increased order.

In food science, starch retrogradation refers to the recrystallization of gelatinized starch molecules after cooling or storage. Gelatinized amylose and amylopectin reassociate into more ordered structures, expel water, and cause gels to firm and bread to stale. The rate depends on moisture, temperature, and storage duration. It can be slowed by maintaining moisture, gentle reheating to re-gelatinize, using fats or sugars, or reducing storage time in the cold.

In geology and sedimentology, retrogradation describes the landward migration of shorelines or sedimentary facies in response to rising relative sea level, forming retrogradational strata. It contrasts with progradation, where deposition builds out toward the sea.

In polymer science, retrogradation denotes slow, post-processing rearrangement of polymer chains that can increase crystallinity or phase separation, influencing mechanical properties and stability in certain biopolymers and hydrogels.

In astronomy, the term retrogradation is sometimes used to describe the apparent backward (retrograde) motion of planets as seen from Earth; however, retrograde motion is the more common term in modern usage.

Overall, retrogradation denotes a backward or reorganizing tendency and is context-specific, with mechanisms and implications varying across disciplines.